1. Field of the Invention
The present invention relates to an improvement in a camera system, and more particularly, it relates to an improvement in an image stabilization system.
2. Description of the Related Art
Cameras have been generally automated in significant operations for shooting images such as exposure setting and focusing. Therefore, even a user inexperienced at operating a camera can achieve good results. In recent years, image stabilization systems have also been widely employed for reducing image blur due to camera shake. Such an image stabilization system of a camera will be briefly described below.
Camera shake during shooting is vibration normally having a frequency of 1 to 12 Hz. The image blur caused by this camera shake is reduced by detecting a shake amount of the camera due to the camera shake, and shifting a correcting lens corresponding to the detected shake amount.
To effectively reduce the image blur due to camera shake, it is necessary to (1) accurately detect the vibration of the camera, and (2) accurately correct a displacement of the light axis due to the vibration. The shake amount of the camera is detected by using angular displacement signals obtained upon integration of signals output from shake sensors that detect an angular acceleration, an angular speed, and the like. A correction optical unit is driven to decenter the shooting light axis on the basis of the accurately detected signals, thereby effectively preventing the image blur.
FIG. 10 shows an example of a camera system provided with an image stabilizer (including an image stabilization optical system and shake sensors) in an interchangeable lens.
A CPU 701 embedded in a camera body 700 and a CPU 703 embedded in an interchangeable lens 702 are connected to each other via a serial bus line with a contact block 704 interposed therebetween.
Actuators (for an aperture, a focusing lens, and the like) provided in the interchangeable lens 702 are driven in response to instruction signals transferred through the bus line from the camera body 700.
The interchangeable lens 702 is provided with shake sensors 705 and 706 for detecting shake around predetermined P and Y axes in the interchangeable lens 702. Outputs from the shake sensors 705 and 706 are converted into outputs having predetermined levels. On the basis of the converted outputs, the image stabilization optical system 707 is driven for image stabilization with respect to the P and Y axes
Circuits 708 and 709 drive the image stabilization optical system 707. A mirror 710 which jumps up in exposure, and a shutter mechanism 711 which determines a shutter speed, are provided in the camera body 700.
FIG. 11 is an explanatory view showing shake waveforms accompanying drive of a focal plane shutter which is used in a normal single-lens reflex camera.
As shown in part (a) of FIG. 11, drive of a shutter front curtain is started. At this time, the camera moves inversely to the movement direction of the shutter front curtain due to the principal of action and reaction. As shown in part (b) of FIG. 11, the downward shake appears.
When a time t has elapsed since the drive of the shutter front curtain was started, the drive of the front curtain is completed, and the movement of the shutter curtain is stopped. Since the camera moves inversely due to reaction, the upward shake appears as shown in part (b) of FIG. 11. Normally, the driving time of the shutter curtain takes several microseconds, and thus the shake due to the drive of the shutter curtain has a frequency of several tens to several hundreds of hertzs.
The shake sensor used for detecting the camera shake is generally difficult to accurately detect a frequency around 100 Hz due to its performance. Owing to this, as indicated by the solid line shown in part (c) of FIG. 11, the peak of the sensor output is displayed by a time ts with respect to the peak of the actual shake waveform.
A correction band of a correction system holds several tens of hertzs to 100 Hz. As a result, as indicated by the dotted line shown in part (c) of FIG. 11, the peak of the output of the correction system is displayed by a time tc with respect to the peak of the sensor output when the sensor output and the shake signal around 100 Hz are compared.
As mentioned above, the actual correction operation is seriously delayed as compared with the shake signal around 100 Hz (ts and tc). Therefore, as shown in part (d) of FIG. 11, the shake waveform on an actual image plane causes increase in image blur due to the delayed correction operation.
To solve the above problem, Japanese Patent Laid-Open No. 9-43660 discloses a configuration in which correction data like a linear function as shown in part (e) of FIG. 11 is added to the output of the shake sensor (see part (f) of FIG. 11), and the image stabilization is performed by using the data.
With this solution, the correction error is reduced as shown in part (g) of FIG. 11. Accordingly, the shake component due to the drive of the shutter front curtain may be substantially corrected.
The above-described publication is designated for the drive of a focal plane mechanical shutter which is used in a normal single-lens reflex camera.
In recent years, digital single-lens reflex cameras have been widely used. There may be a digital single-lens reflex camera that has an electronic shutter function for controlling an exposure time by electrically controlling a light accumulation time to an image pickup device, but does not have a focal plane shutter.
In addition, there may be a camera that has both the electronic shutter and the focal plane shutter, and selects either one of the two types of shutters depending upon a shooting mode or the like. If the technique of adding the shake component due to the focal plane shutter is applied to the digital camera capable of shooting an image only with the electronic shutter, unwanted correction is performed even though there is no shake component due to the focal plane shutter. This may cause the increase in image blur of a captured image.